- The goal of this research is to further understanding of the function of mammalian Hox genes. Key to this is the identification of the genes whose transcription is controlled by a Hox gene (the downstream target genes) since these genes are presumed to effect the observed changes in cell behavior or characteristics controlled by Hox genes. Studies with Ubx suggest Drosophila Hox genes act at multiple levels of a genetic hierarchy. This proposal focuses on use of the hair follicle system for in depth analysis of the developmental roles of and the downstream targets of a single mammalian Hox gene: Hoxc13. Hoxc13 is a good gene for these studies, since the phenotypic consequences of mutation of Hoxc13 in mice suggest it may act at multiple levels affecting proliferation, differentiation, cell lineage decisions, and control of structural protein synthesis. Specific Aim 1 focuses on obtaining direct proof for effects on proliferation, apoptosis, differentiation, and/or cell lineage decisions when Hoxc13 is mutated. Specific Aim 2 strives to determine the identity of genes whose transcription is controlled by Hoxc13 as a further means of identifying components of the genetic hierarchy controlled by Hoxc13. These target genes will be examined to determine whether Hoxc13 similarly acts at multiple levels in the genetic hierarchy first controlling proliferation and differentiation and later in controlling structural protein synthesis. The chromosomal location of these genes will be identified and compared to map locations of mouse hair mutants to determine if the target genes may be mutated in these mice. Mutants so identified will allow further genetic characterization of the pathway controlled by Hoxc13. Since the phenotype of murine Hoxc13 mutants closely resembles that of human patients with ectodermal dysplasias, any genes identified will aid in understanding these syndromes. Finally, Specific Aim 3 will identify Hoxc13 binding sites in chromatin. Spatial and temporal use of Hoxc13 binding sites will be used to assign roles of the target genes in the genetic hierarchy.